The severe loss of photoreceptor cells in retinal degenerative diseases could result in partial or complete blindness. Currently, once the photoreceptors are lost, there is no effective treatment available for restoring lost vision. We are exploring a novel strategy of genetically converting light-insensitive second- or third-order retinal neurons into photosensitive cells, thus imparting light-sensitivity to retinas that lack photoreceptors. Proof-of-concept studies have demonstrated the feasibility of the functional expression of channelrhodopsin-2 (ChR2) and halorhodopsin (HaloR) in inner retinal neurons and resulting restoration of ON and OFF light responses in the retina of a mouse model with retinal degeneration. The objective of this proposal will continue the proof-of-principle studies in rodent models to address issues that are important for developing this treatment strategy for clinical applications. Specifically, we will study the long-term expression of HaloR in inner retinal neurons in vivo and investigate the underlying mechanism(s) of ChR2 and HaloR-mediated light responses in retinal neurons. We will also explore targeted expression of ChR2 and HaloR to specific population(s) of inner retinal neurons and/or sub cellular compartments of retinal ganglion cells. Furthermore, we will investigate the ChR2 and HaloR-mediated light response properties from the targeted cells and their downstream neurons in normal and retinal degenerative mice. Our long-term goal is to develop a novel strategy for treating or curing blindness caused by retinal degeneration. The proposed studies will provide critical knowledge in animal models required for advancing this new treatment strategy to clinical applications. The studies will also advance our knowledge of retinal circuitry and functions under normal and diseased conditions as well as develop new tools for basic retinal research. PUBLIC HEALTH RELEVANCE: Our goal is to develop a novel strategy for treating or curing blindness caused by retinal degeneration. If successful, this strategy could be potentially used to treat or cure all common blindness caused by photoreceptor loss.